The present invention pertains to the art of swivel joints. It finds particular application in conjunction with swivel joints for pharmacy style lamps and will be described with particular reference thereto. It is to be appreciated, however, that the invention may also be applicable to other styles of lamps and other pivotal connections and joints.
Heretofore, pharmacy lamps have commonly included a brass or brass plated steel clutch body which was mounted to a vertical table or floor supported rod. A relatively large diameter passage extended vertically through the clutch body to receive a lower end of an L-shaped metal slide tube which supported a lamp fixture at an upper end thereof. The slide tube was commonly brass or brass plated and lacquered to prevent tarnishing. In order to prevent the clutch housing from scratching and abrading the brass L-shaped slide tube, a plastic sleeve was received within the metal clutch housing to provide a bearing surface. An annular bushing was press fit into one or both ends of the bore to hold the plastic bushing sleeve in place. A knurled metering screw was received in a threaded bore of the clutch housing that extended generally tangentially to the slide tube passage. A rotation of the knurled metering screw caused an angled point to cam against and deform the plastic bushing sleeve. In this manner, rotation of the knurled metering screw selectively controlled the cross section of the bushing sleeve which, in turn, selected the degree of friction with which the brass slide tube was held in the clutch passage.
In any other pharmacy lamp style, the cap for retaining the bushing sleeve within the bore was threaded to the clutch member. Rotation of the cap selectively pressed the sleeve into a cam surface or otherwise compressed it. This selective compression again deformed the clutched sleeve to change its cross section, hence, the degree of frictional engagement with the brass slide tube.
One of the problems with the prior art pharmacy style lamps resided in the complexity of manufacture. In addition to the cost of the many parts, corresponding labor costs were incurred to assemble the separate plastic bushing sleeves into the clutch housing and to anchor it with one or more press bushings or threaded clutch caps.
Another problem with the prior art pharmacy style lamps resided in the tendency for the slide rod to become scratched and marred due to the inadvertent contact with metal parts. Such damage was particularly likely if the plastic sleeve broke or fractured. If the metering screw was screwed down until it pierced or split the plastic sleeve, extensive gouging and damage could occur. Further, rough handling could flex the slide tube into contact with the press bushings or threaded cap for holding the plastic bushing sleeve in place.
The present invention contemplates a new and improved clutch assembly for pharmacy style lamps which overcomes the above referenced problems and others.